NTSC (National Television System Committee) is the analog television system used in the United States, Canada, Japan, Mexico, the Philippines, South Korea, Taiwan, and some other countries (see map). NTSC is also the name of the U.S. standardization body that adopted it.
PAL (Phase Alternating Line) is a colour-encoding system used in broadcast television systems in large parts of the world.
SECAM, also written SÉCAM (Séquentiel couleur à mémoire, French for “Sequential Color with Memory”), is an analog color television system first used in France. A team led by Henri de France working at Compagnie Française de Télévision (later bought by Thomson) invented SECAM. It is, historically, the first European color television standard.
DVR records to a hard drive. Each frame of captured video has a size ranging from 0.5k to 15k depending on the resolution and recording scene. A second of video has a range from 1FPS to 30FPS depending on setting. The size of the video is then decided of its length. Overall, the total size of the video file is ultimately decided by the length and quality. Videos on TV have a frame rate of 30FPS. Although a lower FPS may yield a lower detail of the recorded event, a rate of 7.5 fps is sufficient for most activities, while a rate of 15 fps is sufficient for recording hand movement on cash counters and car license plates. The need of quality is related to the circumstances in which the recording takes place. As videos are being saved onto the hard drive, hard drive slowly loses its capacity for newer videos for storage. Once the hard drive is almost full, software installed in DVR will save the later videos over the oldest, creating a first in first out cycle. The size of the hard drive will be the determinant of how long a video can be saved before it is deleted. However, since the length of video that can be saved onto the hard drive is also depended on the quality, it is difficult to determine the exact length of saved video. Hard drives range from 100 GB to 1TB and the total recording length may range from half a week to one month. It is then up to the customer’s needs for a larger hard drive.
The frames per second (fps) is a measurement of how many pictures are displayed during one second. Real time recording is about 30 fps on a camera, which translates to 30 pictures each second. The total video input FPS would equal the total FPS received by all channels. Then, the FPS on each channel is calculated by dividing the total DVR FPS with total channels. For example, a 30 fps digital video recorder with 2 video channels would result in average about 15 fps per channel.
A network DVR is a DVR with Ethernet connection. This kind of DVR can connect to your own local area network. They can also connect to your DSL or cable modem. Network DVR acts as another network device, similar to a local area printer. However, sharing internet with your computer may require a router.
This is a DVR built based on a computer system. Just as a computer, this system includes motherboard, CPU, video card and other necessary computer components. PC based DVR is usually equipped with a CD burner to backup any recorded video. This system processes videos received from cameras with installed software to provide video compression and storage. Other functions such as camera control, settings can be accessed through the installed PC based software.
A stand alone DVR is an integrated unit of all components on one board. This unit includes a case similar to a VCR, all necessary chips, boards, power supplies, processors and other related components. Videos saved inside DVR may be carried onto a USB or other storage devices. This unit acts all by itself without the need of monitoring or operating.